Manufacture of diolefins



Dec. 18, 1945. H. -J. HEPP MANUFACTURE 0F DILEFINS 2 sheets-sheet 1 Filed Feb. 16, 1942 Dec. 18, 11.945. l H. J. HEPP 21,391,158

MANUFACTURE OF DIOLEFIKNS Filed Feb. 16, 1942 2 Sheets-Sheet'Z HQLVNOLLDVUd ssoPRr-:NE

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PENTADn-:NES PENTAQIENE RECOVERYl HEIZI NVLNBdBG BUTADIENE RECQVERY sEPARA-roR NO LVNO SECOND CRACKI NG STAGE uoivuvdas lsoPRENE HBZINVLNSdBG PENTADIENE sEFARAToR INVENToR HAROLD J. HEPP A'FI'O NE l Patented Dec. 18, 1945 Harold J. nem, Barnesville, Okla., assigner to Phillips Petroleum Company, a corporation of Delaware Application February 16, 1942, Serial Nth-.431,175 2 Claims. (Cl. 260-680) This invention relates to the production of conjugated diolens, and more specifically, toJ the utilization of amylenes as a source of diolens.

Butadiene and related diolens have been found in numerous instances among the products of low-pressure pyrolysis of various simple hydrocarbons, including both' parailins and olens. In general, the dioleln yields reported ,in the literature are low. However, I have found, as the re'- sult of numerous experiments, that enhanced yields of diolens are obtained when the pyrolysis is conducted at a high temperature, with the time of heating limited to periods small enough so that a part of the hydrocarbon being pyrolyzed survives the heating unchanged. The yield of diolens is further improved in some cases if the -pyrolysis is conducted at low pressure or in the presence of diluents such as steam, ue gas,l

- at temperatures above '700 C., and the degree of pyrolysis limited by controlling the time of heat' ing so that not morethan about per cent of the products from the conversion zone. The yield of dioleflns may be further improved, or the amount. of pentene reacted per passage through the heatingzone'increased, with consequent reduction of pentene-rycle,without encountering excessive loss to rpolymers by conducting 'the pyrolysis at`subatmospheric pressure or by reducing the partial pressure'sof the pentenes by the use of diluents such as steam, nue-gas, methane. and the like.

Under the conditions outlined above,the cracking behaviors of pentene-Z and of trimethylethylene are radically different.

Pentene-2 cracks to' butadiene as the major diolen, accompanied by smaller amounts of pentadienes. Trimethylethylene, ontle other hand, yieldsisoprene as the major' dioleiin, ac-

composed largely of a mixture of pentene-Z and' trimethylethylenes, but it is quite difficult to separate pentene-2 and trimethylethylene by distillation or by extraction procedures. Consequently, if it is desired to convert olefin concentrates obtained from sources containing both pentene-2 and trimethylethylene, it will frequently be desirable to treat the olen mixture verted to diolelns by a single step pyrolytic polymers boiling above about 50 C. is present in rather than toseparate the individual oleflns and treat them separately. ,The Wide diierence in the cracking rates of the two olefins leads to the v rather undesirable situation that, if they are conmethod, when conditions of time and temperature are maintained to give optimum conversion of pentene2, only a small percentage of trimethylwhen conditions are maintained to eifect substantial conversion of trimethylethylene,v then the pentene- Z reacts too far to yield -maximum amounts of butadiene.

One aspect of my invention is to provide a two step pyrolytic process for converting such mixtures to diolefns. In the rst pyrolysis step, conditions of time and temperature are maintained in the regionwhere best yields of butadiene 'are obtained from pentene-Z, and the unconverted pentenes from this step, now considerably enriched'in the refractory trimethylethylene, are cracked in a second step under more drastic conditions of time and temperature to yield isoprene.

While the above discussion has disclosed the conversion of mixtures of pentene2 and trimethylethylene, my invention is not limited vto the pyrolytic conversion of such mixtures to diolefins. Trimethylethylene from any source, whether associated with pentene-2 or not, may be efficiently converted to isoprene when pyrolyzed under the conditions outlined above.

The objects of my invention are:

1. To effect the pyrolytic conversion, by a recycle process,v of trimethylethylene into useful and substantial yields of isoprene. p

2. To utilize a hydrocarbon fraction containing flvecarbon atoms per molecule and containing a considerable proportion of amylenes, such as the C5 fraction from typical cracking still gasoline.

3. To produce a conversion feed stock rich in 'thepreferred olens and differing in olefin composition from such a C5 fraction by an economical separating means, and to convert this feed stock by a pyrolytic process to lbutadiene and pentadienes.

4. To convert isopentane to isoprene by an advantageous combination of catalytic dehydrogenation and pyrolytic conversion means.

5. The production of diolens and other byproducts.

Other objects of my invention will be apparent from the following detailed description,

Briey, my invention comprises the conversion of mixtures of trimethylethylene and n-pentenes, to dioleiins by a pyrolytic method.

The economical preparation of aliphatic conjugated doleiins from hydrocarbons of petroleum origin, and particularly the preparation of l butadiene, isoprene, -and piperylene, which are especially suitable for the manufacture of synthetic rubber, has been a very serious problem in the art and has not to my knowledge been entirely satisfactorily solved. The present invention aims to provide a solution of this problem in a simple and economical manner by enabling the production of these diolens from certain of the amylenes.

In accordance with my invention in a broad aspect, a mixture comprising preponderantly or consisting essentially of pentene-2 and trimethylethylene, prepared by any method, is rst cracked under such conditions as to selectively destroy the pentene-2 content forming butadiene, i. e. so that a major portion of the pentene-2 is destroyed or converted to butadiene while the trimethylethylene content is substantially' unaected. l

The uncracked C5 content of the efuent from the rst stage is then passed to a second cracking step where such conditions are maintained as to.

I may involve the same pressure and temperature ranges as given for the rst stage. The timetemperature relationship should be significantly greater. This may be attained by using higher temperature in the ranges given and/or using destroy the major portion or substantially allof I the trimethylethylene' content, forming isoprene.

The selection of the mild and drastic cracking conditions for the first and second cracking stages respectively to attain the desired results will be obvious to those skilled in the art in the light of this disclosure. In general however the first cracking step may be conducted at above '100 up to about 900' C. and preferably from longer contact times. 'I'he conditionsshould be adjusted so that from about 15- 'to about 80% and preferably from about 15 to about 50% conversion of the trimethylethylene content of the feed per pass is obtained. VThe contact time may range from about 0.01 to about 5 seconds.

Other features of my invention involve recycling of butenes from the first stage eiiluent to the rst stage feed, optional use of a common diglen recovery means for both stages, and extraction of butadiene from the rst stage eilluent and isoprene from the second stage effluent.

If it is attempted to crack a mixture of pentene-2 and trimethylethylene in a single cracking step under conditions such as to destroy a major portion of each, the yields of desirable butadiene and isoprene from each is excessively low. The reason for this is that the ideal conditions for conversion of pentene-2 are quite diiferent from those for trimethylethylene. I have discovered that if the mixture is first cracked under conditions ideal for pentene-2, butadiene recovered from.' the efliuent, and the uncracked Cs inthe eiuent (low in pentene-2) cracked separately under conditions ideal for conversion'of trimethylethylene, the yield of de- Isirable diolefins is unexpectedly very much greater andrecovery thereof is easier. I have further discovered that the normally undesirable effect of the presence of the other amylene inv drogenation of isopentane. A large amount of trimethylethylene associated with other amylenes is present vin the hydrocarbon fraction containing ve carbon atoms per molecule obtained from cracking still gasoline. The composition of a typical C5 fraction of cracking still gasoline is roughly as follows: 3-methy1butene-1, 5%; pentene-l, 9%; pentene-Z, 17%; trimethylethylene, 9%; and the remainder predominantly pentanes. The low boiling olens, 3-methylbutene-1 and pentene-l, may be separated from such a mixture, along with isopentane, by fractional dis-1 tillation, or they may be partly isomerized to pentene-2 and trimethylethylene by passing over a suitable catalyst. In this manner, a concentrate of pcntene-Z, trimethylethylene, and n-pentane may be obtained, from which the n-pentane may be separated either by fractional distillation with an -entrainer such as acetaldehyde, propionaldehyde, propylene oxide, and the like,

l ethylene.

or b y solvent extraction with furfural, Miura] alcohol, levulinic, acid and the like. i

However,"the separation of the trimethylethylene andthe `pe'ntene-Z isomersby distillation or extraction procedures. is 'diiiicult As shown in the examples below, the cracking velocity of pen' Atene-2 diiers widely from that oit.Y trimethyl- At a given temperature, pentene-2 cracks about 7 times as fast as trimethylethylene.

Accordingly, .I prefer to pyrolyze mixtures of pentene-2 and trimethylethylene in two steps. In theiirst step, much of the pentene-2 is cracked to yield butadiene and relatively small amounts of pentadienes, while only a small proportion of trirnethylethylene is cracked. The pentenes surviving' the mst step, which are rich in trimethylethylene compared with the starting material, form the feed to the second step. Isoprene, accompanied by relatively small amounts of butadiene and other pentadienes, are produced in the second step.

In the accompanying drawings is shown a ilow diagram illustrating a process for lpreparing a pen'- tene-Z, trimethylethylene concentrateirom aCs fraction containing these oleflns, and converting this concentrate to diolens by a two step pyrim: steppa. separation is-etrect'ed, thecut peint j being in the range of 30 to 34"- pC., and isopen-l \'tane'"containing some low-boiling olefins is passed overhead through pipev23, controlled by valve 24,

5 to cooler 25,.whlch supplies aliquidcondensate for retlux to'column 22,-to pipe 26 and, controlled by valve 21, is recycled to the dehydrogenation system. The high-boiling 'tractionvis recovered as kettle product and passed through pipe 28,

l controlled by valve 29, to pipe 80, or it may be passed through pipe 28a. and valve 28a to pipe 88 and to the cracking coil 1l. -Altemately, the products from -the dehydrogenation of isopentane may be passed directly t0 the solvent extraction l step 32 via pipe I5, valve l1, heat exchangergls,

valve 8| and pipe 30.

The stream from pipe 30, whether from crack'- ing-still or from dehydrogenation products, may be subjected to further separation, such as extraction with furfural, levulinic acid, dimethyl rol'ytic process. The drawings also embrace a forma/mide, furfuryl alcohol, phenolwate'r, and the like. Extraction separation is effected in column 32, under suitable conditions of temperature 'and pressure, and a fraction, composed pre- 5 dominantly of pentanes, pentene-l, 2-methy1butene-1; and 3-methylbutene-1 or such of these hydrocarbons as were introduced to the step, is recovered overhead and withdrawn from the system through pipe 33, controlled by valve 34. Pentene-2 and trimethylethylene, along with solvent.

The feed-stock, which may -.be a C5 lfraction i suchl asmay be separatedfrom cracking-still gasoline *and which contains pentene-2 .and trimethylethylene, is introduced intothe system through pipe I. The feed-stock may be passed @by meansofvalve 2, through heating arrangement 3; wherein the stream is heated to a temperatur'e in the range of 150 to 350 C., and pipe 4 toisomerization step. 5. In* the isomerization step, the stream is contacted with phosphoric acid, aluminum sulfate, or similar catalyst for,.-

a period ,of time, in the range of Z seconds to 3' minutes,sumcient to effect substantial isomeriza- "tion of pe'ntene-l to pentene-2;-`there will be some conversion of unsymmetrical amylene to trimethylethylene.A Y

vAftypical renery Cia-fraction, such as that.

being charged to'the isomerizatlon step, would have about the following composition: 'pentene-l, 9%; pentene-2, 17%; trimethylethylene, 9%; un-

symmetrical lamylene, 5% yand the vremainder predominantly pentanes `Isomeriration lwould eil'ect such conversion that' the ratio of pentene-l to pentene-2 would be about 1 to 10.

The products from the isomerizatim step vare passed through'pifpe 5, controlled byvalve 1, to a fractionating step 8. The Cit-hydrocarbons and y f heavier products are separated as kettle product and withdrawn from the system through pipe 9; 'controlled by valve I0, Pentane-pent'enes and any lighter hydrocarbons present are passed overhead through pipe Il, controlled by valve l2, to

'cooler I3. which supplies a liquid condensate for reflux to column 8, pipe I4- valve i5, pipe I Land heat exchanger I8 to pipe 30, to be subjected to further separation steps.

It desired or convenient, the feed-stock may begproductsobtainedfrom dehydrc'jenation of isopentane in which case it willi-be desirable Ato omit the .isomerlzation step. The feed-stock wouldbepassedfrom pipe Lthrough pipe I6, controlled by-vil I1, pipe I8 ,and heat exchanger 18, pipe 2l 'patrolled by valve 2|, to fractionati are recovered as kettle product and passed through 35, controlled by valve 38, to stripping tower 31. The stripped solvent is recovered as kettle product and may be recycled, by pipe 38,

5 4valve 38, and'cooler 48. to'theextraction step or any portion may be withdrawn fromy thef system through pipe 4I, controlledby valve 42. Pentene-2, trimethylethylene and other hydrocarbons present are recovered overhead and passed 0 through pipe 43, controlled by valve 44, to a cracking step. l

I1' desired, the separation may be .eilected hy means ofazeotropic distillation rather `than by ide, and-the like, is introduced through pipe 4s."

The`

controlled by valve 49, and manifold 50. overhead product, which yiscomposed largely of pentane and entrainer is passed through pipe 5|, controlled by valve 52, to condenserv 53 and accumulator 54. In some cases, a` portion of the entrainer will separate out as a separate phase in .54; when this occurs, the proper amount of each phase is returned to tower 41 through pipe 55 and valve 55. Likewise, when phase separation occurs, excess entrainer phase may be returned e0 to 41 .by means vof pipe 51, valve 58, and pipe 48.

65 the system. Entrainer, enriched with pentene-2 A fraction, which is composed of n-pentanel and low-boiling amylenes such as pentene-l, etc., and which is free of entrainer, is passed through pipe 59, controlled by valve and withdrawn from and trimethylethylene, is recovered asv kettle product and passed through pipe 6|, controlled .by'valve 82, and cooler 53 to tower .54. 'I'he en- 0' able solvent introduced through Vpipe u is recovered as kettle product and withdrawn through pipe 58,' .controlled by .valve 51. Tue desired olens are recovered overhead and passed through 15 vpipe 88, controlled hy valve 48, to pipe 4.3, and

trainer isscrubbed out, with water c r other suitemployed.

a cracking step. Other methods of separating entrainer, such as cooling and decantation may be The pentene-2-trimethylethylene concentrate, prepared as disclosed above, or by other means. from pipe 43 is passed to a heating system which is herein represented by a convection coil, 10,

and a radiationv coil, 1|. Steam or other stable, volatile diluent may be added to the chargestock; from pipe 12 steam, etc., may pass, by

means of valve |3'and pipe 43, directly to the convection coil o! the furnace or it may pass from pipe 12 through pipe 14 to a separate heating coil, 15, and thence through pipe 18, by means of valve p 11, to the convection coil of the furnace or i temperaturesaboveHOO" up to 900 C., and preffrigeration,

erably in the range of 750 to 850 C. The heating time varies inversely with the temperature, decreasing as the temperature is increased, and is adjusted to effect 30 to '70% conversion of the pentene-2 per -pass through the heating zone. The decomposition should be maintained in the lower part of the conversion range when no diluent is used, or when the partial pressure of the. pentene2 is near or slightly above atmospheric pressure. The higher conversions may be effected when the pyrolysis is conducted at pressures below atmospheric, or when diluents such as steam are employed. The total pressure will usually be substantially atmospheric but may range from 0.1 atmosphere to 2 atmospheres.v

The eiiluents from the cracking step are passed from the furnace through pipe 80 to cooler 8|; the cooled eflluents are passed to separation step 82. Polymers and water from the cracking step are withdrawn from the bottom of the separating' column through pipe 83, by means of valve 84. The gases pass overhead, controlled by valve 88, through pipe 85, compressor 86, and cooler 81, to separation step 88. The uncondensed vapors pass overhead through pipe 90,. controlled by valve 8|. to separator 82-wherein C4 and Cs hydro-4 carbons are recovered, as by oil absorption, re-

or similar means and recycled through pipe 83, controlled by valve 84, to a depropanizer, and light gases, hydrogen, methane, and C2 and some C: hydrocarbons, are withdrawn as overhead products through pipe 85, controlled' by valve 88. If separation of C4 and heavier hydrocarbons has been effected to a substantial degree in 88, the separator 82 may be by-passed, as

. through pipe81, controlled by valve 88.

The condensed products are passed from thel bottom of separator 88 through pipe |00, controlled by valve to depropanizer |02. Propane and lighter products are separated overhead and are withdrawn from'the system through pipe |03, controlled by valve |04. The kettle product from the depropanizer is pipeV |05, controlled by valve |08, .to debutanizer |01.

In the debutanizer, the C4 hydrocarbons are recovered as overhead product and are passed, through pipe |08, controlled ,by valve |08, to a separation step,-||0, wherein butadiene is separated from other C4 hydrocarbons.- 'I'his sepal to depentanizer ration may be leilected by any one of several means: fractional distillation may be employed wherein butene-l and isobutylene, if present, are separated in a first step following which butadiene is separated from butene-Z; the separation may be eiiected by an azeotropic fracti'onating step using an entrainer such 'as ethylene oxide, acetaldehyde, and the like, supplemented by fractional distillation. Solvent extraction, employing furfural or other selective solvents, is an especially eilicient method for separating butadiene of high purity.- Or butadiene may be separated and recovered by'reacting the C4 hydrocarbons with sulfur dioxide to form butadiene monosulfone. The butadiene monosulfone formed by the latter method may be separated from the unreacted products by decantation and/or distillation, and the diolefln regenerated by heating the monosulfone to temperatures above about C., and preferably above about C. The reaction between dioletlns and sulfur dioxide may be suitably conducted in the dense phase at temperatures in the range of 30 to 180 C., and preferably in the range of 100 to C.` Inhibitors such as pyrogallol, and/or. Y

phenyl-beta-naphthylamine, may be employed in the low temperature range to avoid the formation of insoluble, refractory polysulfonesV which do not regenerate and diolefln readily, but inhibitors are not necessary at temperatures above about 110 C.,.as polysulfones are formed only in small amounts, if at all, at these temperatures. The time required for completion of the Vsulfone reaction varies inversely with the temperature and Aranges from several days at 30 C. to about 1/2 to 2 hours at 150 C. The sulfur dioxide used may be in the range of 2 to 20- moles per mole of dioleiin. The reaction is a second-order reaction, and the time required is decreased as the amount of sulfur dioxide and/or diolen is increased. The butadiene is system through pipe controlled by valve ||2. The separated butenes are passed through pipe I3 and may bevented from the system by means of valve ||4 or recycled in any proportion to the cracking step through pipe H5, controlled by valve H8, and pipe 80.

The kettle product from debutanizer |01 is passed through pipe ||1, controlled by valve H8, ||8 wherein Ca and heavier hydrocarbons are separated as kettle product and withdrawn from the system through pipe |20, controlled by valve |2 I. "The Cs hydrocarbons are passed overhead from the depentanizer through pipe |22, controlled by valve |23, to separating step |24 wherein isoprene and low boiling oleflns are `separated and passed overhead through pipe |25, controlled by valve |28, and discharged passed through t from the system or subjected to further separation to recover isoprene, yby means not shown, if desired.

The kettle product from |24 may be composed of pentene-2, trimethylethylene, and high boiling pentadienes. If appreciable quantities of pentadienes are present, the kettle product is passed through pipe |21, controlled by valve |28, to separation step |28 wherein pentadienes are separated from unconverted C5 oleflns and withdrawn from the system through` pipe |30, controlled by valve ISI. The separation step, |28, may be bypassed, as through pipe |33 and valve |34, if appreciable quantities of pentadienes are not present. 'I'he unreacted C5 oleilns are recycled through pipe |33 or, if pentadiene separation is withdrawn from the efreeteii, through pipes |32 andlzns, by means of in trimethylethylene, are passed to a .secondl -cracking system which is herein represented by a convection coil, |38, and a radiation coil, |39. Steam or other stable, volatile diluent may be added; .from pipe |40 steam, etc., may pass, by means of valve |4I, directly to the convection coil of the furnace or it may. pass from pipe |40 through pipe |42 to a separate heating coil, |43, and thence through. pipe |44, by means of valve |46, to the convection coil ofthe furnace or through pipe |46, controlled by valve |41, to a radiation coil of the furnace.

The cracking operations are carried out in the y second step under more drastic conditions than in the rst step, i. e., at higher temperatures or for longer times, to eifect more efficient and complete conversion of the refractory trimethylethylv ene. The stream is cracked in the furnace at temperatures of above 700 up to 900 C. and preferably in the range of '750 to 850 C. and for pe'- riods of time in the preferred temperature range of 1.5 to .01 seconds, sucient to eiect 15 to v80% conversion, preferably -15 to 50%, of the trimethylethylene per pass through the heating zone. The cracking conditions are affected by the amount of pentene-Z present and the amount of diluent added.

The eilluents from the second cracking step 35 .system through plpe |94, controlled by valve |95,

leave via line |48 and may be recycled through pipe 80, lby means of valve |149, to the separation" system hereinbefore described. This arrangement effects economies in the separation Vsystem buthas the disadvantage that the products from 'both cracking |steps are intermingled. This results in a decrease in the trimethylethylene con- -v tent 'of the total feed to the second cracking step` and also makes it desirable to remove islobutylene, formedv in the cracking of trimethylethylene, from the recycle butenes. I

The eill'uents from the second cracking step may be m'ore desirably treated in a second separatlon system. The stream is passed from pipe |48 through pipe |50, bymeans-of valve |5|, and cooler l|52 to separation step |53. Polymers and water from the cracking step are withdrawn from the bottom of the separating column through pipe |54, by means of valve |55. The gases pass overhead, controlled by valve |59, through pipe |58, compressor |51, and coolerA |58, to separation step |60. lThe uncondensed vapors pass overhead through pipe |6|, controlled by valve |6|A,

to separator |82 wherein C; and C5 hydrocarbons are recovered, as by oil absorption, refrigeration, or similar means, and passedvthrough pipe |63, controlled by valve |64, to a depropanizer |1l. and llghtgases are withdrawn overhead and discharged from the system through pipe |65, controlled by" valve |86; The separator, |62, may be by-pa'ssed as through pipe |61 and valve |38.

The condensedproducts are passed from the bottom'of separator. |80 through pipe |69, controlled by valve |10, to depropanizer |1|. Propane and lighter-products are .separatedover-I 79 yields of 6.4'to 10.7 per cent wererobtained from pentene-2. Unlike pentene-Z, trimethylethylene head andare withdrawnfrom the system through In the debutanizer, C4 hydrocarbons arev recov-` 20 of isoprene and other pentadienes.

5 fected -by solvent extraction, azeotropic distillation or sulfone formation. Butadiene is recovered, as through pipe |80 and valve |8|. The

separated butenes are withdrawn from the system through pipe |82, controlled by valve |83. In most cases, this stream will be undesirable as a recycle stock .because of the high concentration of 'isobutylene Removal of isobutylene, as by selective' catalytic polymerization or by HC1 reaction, or by other means would be necessary.

to prepare the sti-earn for recycling to heater 10.

The kettle product from the debutanizer may be passed through pipe |84, controlled by valve |85, to pipe Ill and "the depentanizer,1|9, to be treated as hereinbefore described for recovery bination, while .diluting the stream to .the piperylene-separation step, may be advantageous in some cases.

The kettle product from debutanizer |16 may be passed from pipe |84 through pipe |86, by

means of valve |81, to depentanizer |88. Cs and heavier hydrocarbons are separated as kettle product and are withdrawn from' the system through pipe |89, controlledby valve |90. The

3o C5 hydrocarbons are passed overhead from the depentanizer through pipe |9|,'1 controlled by v'valve |92, and through valve |92A to separating step |93 wherein isoprene and low-boiling olens are recovered overhead and discharged from the or aresubjected, if desired, to further separation means not shown to recover isoprene.

v The kettle product from |93 is passed through pipe |96, controlled by valve |91, to separation 40 step |98 wherein pentadienes are separated from unconverted C5 olefins andare withdrawn from the system through pipe |99, controlled by valve 200. The unreacted olens from the separation step |98 or, if this separation step is by-passed through pipe 20| and valve 202, the unreacted olens from the separation step |93 are passed through pipe. 203, controlled by va1ve.204, are recycled through pipe |36 to the second cracking step. Alternately, the overhead product from |88 `may pass directly to separation step |98 via |9| 'and valves |92 and |92B, where total pentadienes are recovered.

It is to be understood that al1 columns are equipped Withpumps, heat exchangers, heating coils, overhead condensers and reuXv return and, where necessary, points of entry of solvent 'of'. entrainer that, Athough omitted here to simplify the ow-sheet,'are knowndto the art and are used commonly as a part of the equip- ,50 ment for such operation as herein described.

EXAMP` LEs by passing through heated tubes of negligible catalytic activity under conditions .of time and temperatureas' Vshownl in the following table. vutadiene yields ranging from 26 to 34 per cent by -weight of-the pentene reacted, and pentadiene yielded only 4 per cent oi butadiene. However, ,isoprene amounting to`40 per cent by weight of the trimethylethylene reacting were obtained.

,15 IDetailed data are given in the following table.

This coments. With-diluents, a. higher decomposition per ,emciency. The 'amount of Products of paralysis of pentenes Example No.

H. C. charged Average temperature Total pressure-mi11imeters Time (sec.) Steam/H. C. ratio Percent reacted Reaction velocity constants (k) Yield CHt based on H10 reacts Yield CiBn based on 05H10 reacted 2-Mc-butene-2 12g? F. (779 CJ--.

Pentene-2 14.31 F. (778 0.).-- 745 Comiosition of products (weight percent):

Carbon Total l l Diiierence in total and 100.0 is the CO and CO, found in the cluent grs.

The cracking conditions used may be governed 30 by the following considerations.

For the feed to the cracking unit in the first stage, the time-temperature relationship to obtain from to 70% cracking of pentene-Z perI pass is determined by the following Equation 1 (1) 10g =1--:l.9@ (14.851037) where t is reaction time in. seconds and T is cracking temperature in degrees Kelvin.

For the feed to the cracking unit in the second stage the most useful range is 15 to 50% by weight of trimethylethylene cracked per pass. The following Equation 2 covers the time-temperature relationship for this region:

VThe exact amount of decomposition selected` depends upon the presence or absence or dilupass may 'usually be employed without loss of decomposition also depends upon the temperature used. Thus, in the lower temperature ranges, the extent of decomposition per pass willusually be maintained in the lowerrportion of the range of per cent cracked. i

' I claim: v

' 1. The process for the production of dfoleflns from a mixture of pentenes comprising pentene- 2 and trimethylethylene which comprises subjecting said mixture to p yrolysis in a firstzone. at. substantially atmospheric pressure and at a, temperature within the range of 700 C. to 900 C.' for a period of time sumcient to convert from to 70 per cent of the pentene-2 content of said mixture to other materials with optimum yield of butadiene; separating theY butadiene so formed from the eluent of said first zone; and .m

subjecting the mixturefof unreacted pentene-2 and trimethylethylene contained in the eilluent ofv said ilrst zone-t0 pyrolysis in 'a second zone at substantially atmospheric pressure and at' a temperature within the range of 700 to900 C. for a period of time materially greater than that employed in the first zone and sufiicient to convert from 20 ylethylene content of said mixture of unreacted pentene-2 and trimethylethylene to other materials with an optimum yield of isoprene.

2. The process for the production of diolefins from a mixture of pentenes comprising pentene- 2 and trimethylethylene which comprises subjecting said mixture to pyrolysis in a. first zone at substantially atmospheric pressure and at a temperature within the range of '700 C. to 900 C. for a period of time within the limits defined by the following Equation 1:

log t= where t is the reaction time in seconds and T is` acted pentene-2 and trimethylethylene contained in the eiliuent of said first zone to pyroly- V sis in a second zone at substantiallly atmospheric l pressure and at a temperature within the range of '100 C. to 900 C. for a period of time in excess of that employed in the rst zone and within the limits defined by the following Equation 2:

, where t is the reaction time in seconds and T is the temperature in'degrees Kelvin, under conditions such that from 20'to 80 per cent of the trimethylethylene content o! said mixture of unreacted pentene-2 and trimethylethylene is converted to other materials with optimum yield of isoprene.

nanou) J. mi.

to per cent of the unreacted trimethrst. `zone; and subjecting the mixture of unre-v 

